Avoid unnecessary linked list traversals in MethodLinker.

The chains themselves are assumed to be an implementation detail of this class, in which case it's fine to flatten them at any time.

base/src/main/java/proguard/classfile/util/MethodLinker.java

@@ -19,7 +19,9 @@
 
 import static proguard.classfile.instruction.Instruction.OP_INVOKESTATIC;
 
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import proguard.classfile.AccessConstants;
 import proguard.classfile.Clazz;
@@ -132,12 +134,19 @@ private static void link(Member member1, Member member2) {
    * @return The last method in the linked list.
    */
   public static Member lastMember(Member member) {
+    List<Member> chain = new ArrayList<>();
     Member lastMember = member;
     while (lastMember.getProcessingInfo() != null
         && lastMember.getProcessingInfo() instanceof Member) {
+      chain.add(lastMember);
       lastMember = (Member) lastMember.getProcessingInfo();
     }
 
+    // Point every member in the chain directly to the last element to save time in the future
+    for (Member relatedMember : chain) {
+      relatedMember.setProcessingInfo(lastMember);
+    }
+
     return lastMember;
   }
 
@@ -149,6 +158,9 @@ public static Member lastMember(Member member) {
    */
   public static Processable lastProcessable(Processable processable) {
     Processable lastProcessable = processable;
+    if (lastProcessable instanceof Member) {
+      lastProcessable = lastMember((Member) lastProcessable);
+    }
     while (lastProcessable.getProcessingInfo() != null
         && lastProcessable.getProcessingInfo() instanceof Processable) {
       lastProcessable = (Processable) lastProcessable.getProcessingInfo();